O'Reilly's Brady Forrest reports that the folks at Urban Mapping have just made the neighborhood lookup functions of their web service API free. Urban Mapping provides a useful piece of the online geographic puzzle by providing detailed data on over 1,000 municipalities and more than 20,000 distinct neighborhoods. The API is a SOAP-based service that lets you find the names of neighborhoods based on lat-lon coordinates, city or postal code. We've have updated our Urban Mapping API Profile here.
Note that a couple of comments on the O'Reilly post from sharp developers Adrian Holovaty and Chandu Thota add to the discussion, pointing out that the API does not (yet) provide polygons for the underlying data and it does not use standardized neighborhood IDs. In his own post, Chandu notes that the latter is a more general problem, not Urban Mapping specific: "This is not an issue with Urban Mapping API per se, but they expose neighborhood IDs that are proprietary to them. What we need is a standard-based way to identify neighborhoods, some sort of taxonomy you know. For example, the neighborhood that is identified as "17476" in Urban Mapping API is not the same neighborhood in some other dataset. So if I'm building a mashup with neighborhood data, I want it to be portable (more on the map APIs and portability later)."